However, large bar size placement cost is smaller than the installation cost of large number of small bar sizes. This is because such bars cause flexural cracking and required greater length to develop their strength. Generally, it is advised to avoid the use of large bar sizes for beams. Lastly, it is recommended to use 0.6*maximum reinforcement ratio. Nonetheless, the choice is influenced by ductility requirement, construction and economic consideration. So, any values between this range can be used for beam design. The reinforcement ratio is an indicator of the amount of steel in a cross section. The width of the beam shall be equal or less than the dimension of the column supporting the beam.ĪCI 318-11 provided minimum and maximum reinforcement ratio. So, minimum bar spacing shall be considered while beam width is estimated. The reinforcement arrangement is one of major factors that specify beam width. The ratio of beam depth to its width is recommended to be between 1.5 to 2 with upper bound 2 being the most common used. Table 2 span to depth ratio based on the span and type of beams, IS 456 2000 IS 456 2000 provides span to depth ratio to control deflection of beam as provided in Table 2. The depth of beam can also be estimated based on span/depth ratio.For other conditions, the values modified as follows:Ī) For lightweight concrete having equilibrium density ( wc) in the range of 1440 to 1840 kg/m3, the values shall be multiplied by (1.65 – 0.0003 wc) but not less than 1.09.ī) For fy other than 420 MPa, the values shall be multiplied by (0.4 + fy/700). Values given shall be used directly for members with normal weight concrete and Grade 420 reinforcement. Members not supporting or attached to partitions or other construction likely to be damaged by large deflections
Table 1 minimum thickness of non-prestressed beams unless deflections are calculated Canadian Standard Association (CSA) provides similar table except for one end continuous which is l/18.ACI 318-11 provides suggested minimum thickness for non-prestressed beams unless deflections are calculated.However, certain guidelines can be followed to compute beam depth such that the deflection requirements can be satisfied. There is no unique procedure for computing overall beam depth(h) for design. It should be known that, experience of designer plays significant role in making these assumptions. these guidelines are provided by certain codes and researchers. Prior to the design of reinforced concrete beam begin, there are certain assumption that need to be made. The First approach will be presented below.Design of rectangular reinforced concrete beam procedure.
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